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Post by connorfixesstuff on Jun 22, 2020 23:12:09 GMT -5
Hey guys, I’m new to the forum, and relatively new to fixing scooters. I have a 49cc Vento triton r4, and it has 7000ish miles. It’s running with bad compression and no gas at the spark plug. I thought the carb might be bad so I cleaned it with carb cleaner and eventually replaced it. Still had no gas. I thought it might be a vacuum problem, so I looked into the compression. I bought a compression tester and it was at 120 psi (The manual says limit is 139). So I bought a cylinder kit for a Honda jog 50, which was basically the same cylinder I think, 40mm bore, same exhaust port, minarelli, same fundamentals. The wrist pin was too small for the existing needle bearing, so I made my own. Oiled it up and it fit snug. I did a another dry compression test after assembly and tested at 90psi. I did a wet compression test and it got to 150 psi! I’m pretty sure the rings are at fault but thing is they are new. Again it has low compression and is running lean. Help!
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Post by connorfixesstuff on Jun 27, 2020 17:41:19 GMT -5
I also had a cylinder base/crankcase gasket come in the cylinder kit, does it affect compression at all? I read something about it affecting the squish height or something.
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Post by aeroxbud on Jun 27, 2020 21:13:37 GMT -5
Gaskets come in different thickness. So a thinner gasket would make the piston nearer the top of the head. Giving higher compression.
Running lean is usually a sign of an air leak somewhere. Check for bad sealing or cracks in the rubber manifold.
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Greg
Scoot Enthusiast
Posts: 218
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Post by Greg on Jun 28, 2020 8:18:02 GMT -5
Harbor Freight compression tester?
If you gt anything over about 100 PSI with a Harbor Freight tester you should be fine.
The Harbor Freight tester has a hose that is too long to accurately measure compression. The stroke of our scooter engines is so small the HF tester (or any tester with a foot long hose) can't get an accurate reading. To anybody who has a HF compression tester, and a more accurate tester - comparing the numbers could make a great write-up in the tech section.
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Post by connorfixesstuff on Jun 28, 2020 10:17:15 GMT -5
Gaskets come in different thickness. So a thinner gasket would make the piston nearer the top of the head. Giving higher compression. Running lean is usually a sign of an air leak somewhere. Check for bad sealing or cracks in the rubber manifold. How do I check for air leaks and where do I check? Also, when you say rubber manifold, do you mean the rubber thing that goes from the carb to the reed valve? Thanks for replying guys! I’m happy that other people are on this. |
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Post by aeroxbud on Jun 28, 2020 10:45:55 GMT -5
Yes the manifold from carb to reeds is a common area for leaks. Where the rubber goes hard. But also because the carb gets removed as well.
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Post by FrankenMech on Jun 28, 2020 19:03:41 GMT -5
Rings also take a while to seat lowering compression at first.
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Post by connorfixesstuff on Jun 28, 2020 19:27:52 GMT -5
Rings also take a while to seat lowering compression at first. How long do you think till the seat in/break in? |
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Post by connorfixesstuff on Jul 10, 2020 13:46:28 GMT -5
AMAZING UPDATE.
It runs, but only when I start it with an open throttle. That was after I made to intake gaskets out of paperboard from a box to a flywheel puller kit. I don’t know what it means, but yeah.
I’m going to replace the crank seals, cylinder base gasket, and intake gaskets (between the reed valve and the crankcase, and between the reed valve and the intake manifold).
Any thoughts on this topic will help, thanks in advance!
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Post by Mech Warrior on Jul 10, 2020 18:09:14 GMT -5
Connor you can watch some of 49ccscoot you videos to see a few tips and tricks for installing and setting up proper.
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Post by connorfixesstuff on Jul 12, 2020 13:29:57 GMT -5
Ok I replaced the cylinder base gasket and it starts without open throttle, but it only runs on high idle, and surges.
Is it still an air leak?
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Post by Zino on Jul 12, 2020 14:38:58 GMT -5
Surging is a symptom of air leak.
Most likely between the carb and the engine
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Post by connorfixesstuff on Jul 18, 2020 17:28:29 GMT -5
Update
The surging was fixed, it will also run on normal idle speed
It revs up but stalls when accelerating and the scooter won’t move very much
Is this because of the 90psi compression? Also, I’m thinking that I’m going to replace the cylinder with a 70cc big bore, would that be a good idea?
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Post by aeroxbud on Jul 18, 2020 18:33:01 GMT -5
That's not a lot of compression. Something is not right. How many miles does the engine have on it? Was the base gasket the same thickness as the one you removed?
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Post by connorfixesstuff on Jul 18, 2020 18:42:33 GMT -5
Yes the base gasket was the same thickness
Also it has 7000ish miles on it
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